Catalytic ignition means for a jet engine thrust augmentation system



Nov. 10, 1964 D. o. NASH ETAL CATALYTIC IGNITION MEANS FOR A JET ENGINE THRUST AUGMENTATION SYSTEM Filed NOV 21, 1962 T El puma-r $7595.95. Ja/m/ 2 Pl 1/4 64 A a/44y C" W United States Patent 3,156,094 CATALYTIC IGNITION MEANS FOR A JET EN- GINE THRUST AUGMENTATION SYSTEM Dudley O. Nash and John P. Plungis, Cincinnati, (ihio,

assignors to General Electric Company, a corporation of New York Filed Nov. 21, 1962, Ser. No. 239,233

4 Claims. (Cl. flit-39.82)

, This invention relates to an improvement in jet engine thrust augmentation systems in general and, in particular, to catalytic ignition means for such a system having an improved service life and the capability of easy replacement.

In the continuous flow combustion systems of the type encountered in turbojet thrust augmentors or, as they are commonly called, aftenburners and in ramjets, difficulty has been encountered in initiating and sustaining combustion during certain flight conditions. For example, at low, local exhaust duct fuel-air ratios combustion may often be sporadic instead of stable, as desired, while at low density, high velocity conditions the flame once initiated may be easily extinguished due to the combined effects of quenching and low reaction rate. It is well known in the art that catalytic ignition devices may provide a solution to these problems. 'While the use of a catalytic material, suchas platinum or a platinum containing alloy, to enhance combustion has been known for some time, as evidenced by, for example, the patents to Bock2,194,081 or Guyer--2,256,657, it has only been within the last decade that the use of catalytic ignition means has been suggested for use as a solution to the problems inherent in jet engine combustion. Examples of the more recent discoveries in this field may be found in the patents to Berl 2,970,439, Allen-2,972,227, Meyer et al.-2,929,2=1l, and Vdovi-ak3,032,99l, the latter being assigned to the assignee of the present application.

However, these prior art systems have often left something to be desired. For instance, as pointed out in the co-pending application of common assignment, Serial No. 156,088, filed November 30, 1961, one of the primary problems centers around the ways in which the life of the catalytic material can be extended. For example, as shown in the patent to Toone--2,964,907, platinum catalyst screens have evidenced a tendency to break loose or burn out after short usage when subjected to the high temperatures and high velocities of the exhaust gas stream of the more advanced jet engines. It is also difiicult when the catalytic element is located within the confines or immediately downstream of a flameholding device to predict the temperature variations and the amount of turbulence to which the element will be subjected. As pointed out in the referenced co-pending application of common assignment if, on the other hand, the catalytic element is exposed to the direct how of the combustible gas stream it will be necessary to provide means whereby the element is sufiiciently protected from the stress and strain caused by the high velocity, high temperature gas striking the element. Therefore, the typical prior art catalytic ignition means, including the mounting or support arrangements therefor, have been less than optimum with regard to extended life and ease of replacement.

Accordingly, it is a primary object of the present invention to provide an improved catalytic ignition means having an extended operational life for use in a high temperature, high velocity continuous flow combustible gas stream, suchias is found in a jet engine afterburner.

A more specific object of the present invention is to provide a catalytic ignition means and mounting therefor wherein cooling flow around the catalytic material and holder is enhanced and replacement of the catalytic mateice rial, when it has deteriorated suificiently through use, is greatly simplified.

A further object of the present invention is to provide an improved catalytic ignition means in which the catalytic material or element is held in place by a dynamic loading torce arrangement whereby the wear factor on the element during operation is reduced and maximum efliciency is maintained during the life of the element.

A still further object of the present invention is to provide a mounting arrangement for a catalytic igniter element whereby the force of the high velocity hot gas stream impinging on the element will be maintained at a substantially uniform constant pressure during the operational life of the element to help to increase element life.

In carrying out the aforementioned objects, a preferred embodiment of the invention comprises an improved cat-alytic ignition device having a main body portion, a support member positioned within the body portion, a center bore through the support member, a plurality of diverging cooling air passages arranged normal to the flow direction of a hot gas stream passing through the center bore, with an annular space provided between the support member and the body portion in flow communication with the passages, and a flow-permeable catalytic element located in the support member and positioned in the path of the hot gas stream. A free-floating, perforated metering disk is arranged in overlying relationship with the catalytic element. With this arrangement, the metering disk is dynamically loaded against the catalytic element so as to ensure a sub stantially constant gas stream load upon the catalytic element, regardless of the effect of the hot gas stream tending to reduce the dimensions of the element, and to prevent flow fluctuations which have been shown to have a tendency to reduce life. The parts of the described catalytic ignition device, including the supporting members, are maintained in an assembled relationship by removable retainers which enable easy replacement of the catalytic material or element.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. However, as regards its organization and operation and further objects and advantages thereof, it is believed the invention may best be understood by reference to the following description when taken in connection with the accompanying drawings in which:

'FIG. 1 is a side elevation view of a jet engine exhaust pipe in which is mounted afterburning or thrust augmentation combustion apparatus in combination with the improved catalytic ignition means of the subject invention;

PEG. 2 is an enlarged side view, partially in cross-section, of the improved catalytic ignition means indicating the manner in which it is mounted to the flameholder means shown in FIGURE 1;

FIG. 3 is an enlarged end view illustrating the direction of cooling flow through the improved catalytic ignition means of the present invention; and

FIG. 4 is an exploded, assembly View illustrating the components comprising the supporting portions of the catalytic ignition means and the placement of the catalytic element and retaining means.

Turning now more specifically to FIGURE 1, depicted schematically is a jet engine tailpipe or exhaust duct having an outer casing or shell 10. The tailpipe may include an annular center body 14 which divides the exhaust area into an annulus through which flows a stream of hot combustible gases indicated by the solid arrows, which gases exit from the exhaust duct in the form of propulsive jet. As is the case in most thrust augmenting systems, fuel injection means 16 is provided which projects transversely of the combustible gas stream. It is also commonto use a flame stabilizing device, such as the annular flameholder assembly indicated generally at 18 inserted in the combustible gas stream downstream of the fuel injection means. The fiameholder annular gutters typically are V-shaped in cross-section. Affixed to one of the V-shaped gutters and indicated generally at 20 is the improved catalytic ignition means which comprises the subject of the present invention.

Turning to FIGURE 2, the invention is described in more detail in an enlarged view. As shown in the drawings, it will be apparent that the igniter of the subject invention, like the great majority of the prior art igniters, will be subjected to a constant fuel-air mixture across its entire width. This results in severe heat generation and a corresponding tendency towards reduction of heat dissipation, which ultimately leads to reduction in igniter life unless steps are taken to improve the design. As described herein, our improved catalytic ignition means 20 includes a cylindrical body portion or sleeve 21 having imperforate walls. The sleeve is permanently attached to the fiameholder gutter by welding or brazing and extends in an upstream direction with its axis substantially parallel to the jet engine duct centerline 10. The body or sleeve 21 includes an internal shoulder portion 22 which is adapted to abut a holder or support member indicated generally at 24. The holder member comprises a reduced cylindrical portion 26 extending in an upstream direction from an enlarged downstream portion 28. The downstream portion 28 contacts the upstream face of the shoulder portion 22 and thus is retained in the cylindrical sleeve 21 against the force of the gas stream flowing in a direction indicated by the large arrow. The enlarged portion 28 of the holder member 24 also has a central opening 30 through which the hot gas stream will pass. The opening 30 communicates with an internal bore 34 in the upstream portion of the holder member in which is adapted to be positioned the catalytic material or element. In the form shown in the drawings the catalyst comprises a plurality of platinum or platinum containing alloy disks or circular pieces of small wire mesh arranged in a pad or core 36. The pad 36 could also comprise a single flow permeable member having substantial thickness in the direction of flow. Deposited upon the surfaces of the core or pad 36, or in the form of separate disks or wafers, are insulating means 38-38, one of which is located on the upstream side, the other on the downstream side. Thus, the element is cylindrical, substantially wafer-like, and rests within the internal bore of the holder member on the surface 39.

Upstream of the insulating means on or in front of the catalytic element 36 is located a metering disk 40 having a plurality of openings 41. While it is well known in the prior art to provide some sort of retaining cover or cap to prevent the catalytic element from being blown out by the high velocity gas stream, heretofore such covers or caps have been rigidly fastened to or supported within the catalytic element support means. However, it will be noted that in the present invention, the metering disk 40 merely rests against the platinum pad or core pieces being dynamically loaded thereon by means of the force exerted by the gas flow. While previous designs allow the platinum or platinum containing alloy element(s) to flutter and shift about in the holder, and therefore suffer damage ranging from harsh abrasion to complete loss of structural continuity of the element(s) or, on the other hand, rigidly clamp or secure (e.g., brazed) the element(s) to the holder, which results in difficulty in replacing a damaged or worn out element, the present invention utilizes dynamic pressure loading on the metering disk to maintain the catalytic element against the shoulder 39. Thus, contrary to the conventional design wherein the mechanical clamping methods eventually lose their effectiveness by reason of, for example, the platinum mesh or screen increasing in compactness under the combined forces of time and temperature, the pressure loaded, floating metering disk of the present invention is free to move as the screen or mesh pad becomes compacted and this maintains a constant level clamping force during the life of the catalytic element. With this feature the improved catalytic ignition means described herein has shown not only to be capable of longer operational life but the design has made possible more consistency of life among a multiplicity of catalytic ignition means utilized in a significant number of production type jet engine installations. In this manner, although other methods have been suggested whereby the life of a specific igniter has been improved, up until the present invention attainment of consistency in igniter life has been lacking.

Returning again to FIGURE 2, there will be seen another feature of our invention which concerns an improvement in cooling flow designed also to prolong igniter life. It will be seen that the upstream portion 26 of the holder member 24 is smaller in diameter than the inner diameter of the body member 21 upstream of the shoulder 22. This provides an annular fiow passage 42 around the outside of the holder member. In addition, there is provided a plurality of diverging cooling air passages 44 at the downstream end of the reduced portion 26 of the holder member, i.e., the passages are located between the reduced portion and the enlarged portion 28 of the holder member 24. As perhaps better indicated by FIG- URES 3 and 4, the passages extend from the bottom or downstream end of the annular flow passage 42 to the center bore 30 of the holder member, i.e., normal to the gas flow through the igniter means. As shown by the small arrows in the drawings, the airflow, after passing through the annular passage 42, exits through the diverging passages, cooling the holder and the periphery of the center bore since the passages 44 merge into an annulus adjacent the rim of the center bore 30. The described arrangement provides a unique, more efiicient cooling flow path for the catalyst holder 24, wherein the cooling air is directed radially inward through diverging passages and discharges as a cooling film over the periphery of the center bore in the holder through which passes the hot gas stream. It has proved to be capable of eliminating substantially all severe jet engine afterburner catalytic igniter burning problems.

Still another feature of the present invention is the means whereby the catalytic element can be easily replaced. Experience has shown that the catalytic element, which in the preferred form comprises one or more platinum or platinum containing alloy mesh or gauze pads, slowly deteriorates with use. That is, the diameter of the fine platinum wires comprising the mesh will be slowly reduced with use which will result in reduced catalytic activity and further loss of platinum. Thus, one of the objects of the present invention is to develop means for easily and periodically reloading the catalyst holder with a new element without the need for destroying the supporting body members or holders or requiring a complicated disassembly procedure. In the embodiment shown, there is provided a plurality of removable retainer means in the form of wire clips generally indicated at 48. These clips pass through holes in the holder member 24 and are adapted to be bent over at 49 and 59 at opposite ends to provide loose retention of the metering plate in the platinum catalytic element. While holding the elements of the catalytic igniter means in an assembled relationship, there is still permitted the dynamic loading feature, utilizing the metering disk 40, described above.

FIGURE 4 also illustrates clearly the manner in which the catalytic element or pad 36 and the metering disk 46 are easily assembled using the clips or retainers 43. Another advantage gaincd through easier replacement of the catalytic element is maintenance of a high level of catalytic activity since the platinum gauze or mesh is more likely to be replaced periodically before an unwarranted amount of loss of catalytic activity has taken place through reduction of the amount of the catalytic material in the element. A by-product of this arrangement is the economic advantage realized by the ability to utilize the used platinum in the element replaced since it usually comprises about 80% of the cost of new material of the new element. With the conventional igniter, wherein the catalytic element is rigidly clamped or welded at assembly to the holder, replacement of the holder and/or the element is impossible, or at least impractical.

Obviously other modifications and variations of the present invention Will be possible in light of the above teachings. It is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What we desire to claim is:

1. An improved catalytic ignition device for use in a high velocity, continuous flow combustible gas stream, said ignition device comprising:

a generally cylindrical hollow body member having an imperforate wall and including a shoulder located internally and intermediate the open ends thereof;

a support member positioned within said body member and including a central opening therethrough, said support member forming an annular passage with the interior surface of said imperforate wall;

a plurality of diverging passages in flow communication with said annular passage and said central opening;

a flow permeable element of catalytic material positioned in said support member in the path of the combustible gas stream;

a free-floating perforated metering disk overlying the catalytic element and presenting a surface normal to the gas stream, said metering disk being dynamically loaded against the catalytic element by the force of said gas stream flowing axially through said openended hollow body member;

and removable means retaining said disk in a loosely assembled relationship with said support member to permit immediate replacement of a damaged or worn out catalytic element.

2. An improved catalytic ignition device for use in a high velocity, axial-flow combustible gas stream, said ignition device comprising:

axially-directed open-ended annular imperforate wall means located in said gas stream;

a support member retained in said Wall means, said member having a central opening therethrough;

a pad of catalytic wire mesh positioned in said support member so as to be permeated by said combustible gas stream;

an insulated, rigid wire screen downstream of said pad;

an insulated metering disk upstream of said pad, said wire screen and said disk retaining said pad against the gas dynamic loading in such a manner as to keep the force of the axially flowing gas stream tending to compress said pad substantially constant;

a plurality of cooling fiow passages in said support member, said passages being in flow communication with said central opening;

and removable retainer means maintaining said disk and said screen in a loosely assembled relationship with said support member to enable immediate replacement of said pad.

3. In a jet engine exhaust duct containing a high velocity, continuous flow combustible gas stream:

imperforate, continuous Wall means arranged parallel to the direction of flow;

an axially-extending support member located within said well means and coaxial thereto, said support member and said wall means forming an annular cooling flow passage, said member having a central bore therethrough;

a catalytic element of compactible material located in said support member bore;

a plurality of diverging passages connecting said annular passage and said central bore downstream of said element;

a free-floating member in said central bore, said freefloating member being dynamically loaded against said compactible element by the gas stream;

and a plurality of removable retainer means maintaining said free floating and support member in an assembled relationship with said element and said wall means.

4. An improved catalytic ignition device for use in a high velocity, continuous flow combustible gas stream, said ignition device comprising:

a generally cylindrical body portion having an imperferate wall, said body portion being open at either end and including a shoulder internally thereof;

a support member positioned within said body portion, said support member having an enlarged portion adapted to be positioned against said shoulder and a reduced portion extending upstream thereof;

a center bore through said enlarged and reduced portions of the support member;

a plurality of circumferentially spaced diverging passages adjacent the boundary of the enlarged and reduced portions, said passages being normal to the flow direction of the gas stream passing through the bore;

an annular passage between the support member and the cylindrical body portion wall, said passage being in flow communication with said bore through said diverging passages;

a flow permeable, compactible element of catalytic material in said support member bore in the path of the gas stream;

a free-floating perforated metering disk overlying the catalytic element and having a face normal to the gas stream, said metering disk being dynamically loaded against the catalytic element by the force of the gas stream;

insulating means between said element, said disk and said support member, respectively;

and removable means loosely retaining said disk in an assembled relationship with said support member so as to permit immediate replacement of a damaged or Worn out catalytic element.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,742 Suter et a1. Nov. 10, 1953 2,964,907 Toone Dec. 20, 1960 2,970,439 Berl Feb. 7, 1961 2,972,227 Allen Feb. 21, 1961 3,032,991 Vdoviak May 8, 1962 

1. AN IMPROVED CATALYTIC IGNITION DEVICE FOR USE IN A HIGH VELOCITY, CONTINUOUS FLOW COMBUSTIBLE GAS STREAM, SAID IGNITION DEVICE COMPRISING: A GENERALLY CYLINDRICAL HOLLOW BODY MEMBER HAVING AN IMPERFORATE WALL AND INCLUDING A SHOULDER LOCATED INTERNALLY AND INTERMEDIATE THE OPEN ENDS THEREOF; A SUPPORT MEMBER POSITIONED WITHIN SAID BODY MEMBER AND INCLUDING A CENTRAL OPENING THERETHROUGH, SAID SUPPORT MEMBER FORMING AN ANNULAR PASSAGE WITH THE INTERIOR SURFACE OF SAID IMPERFORATE WALL; A PLURALITY OF DIVERGING PASSAGES IN FLOW COMMUNICATION WITH SAID ANNULAR PASSAGE AND SAID CENTRAL OPENING; A FLOW PERMEABLE ELEMENT OF CATALYTIC MATERIAL POSITIONED IN SAID SUPPORT MEMBER IN THE PATH OF THE COMBUSTIBLE GAS STREAM; A FREE-FLOATING PERFORATED METERING DISK OVERLYING THE CATALYTIC ELEMENT AND PRESENTING A SURFACE NORMAL TO THE GAS STREAM, SAID METERING DISK BEING DYNAMICALLY LOADED AGAINST THE CATALYTIC ELEMENT BY THE FORCE OF SAID GAS STREAM FLOWING AXIALLY THROUGH SAID OPENENDED HOLLOW BODY MEMBER; AND REMOVABLE MEANS RETAINING SAID DISK IN A LOOSELY ASSEMBLED RELATIONSHIP WITH SAID SUPPORT MEMBER TO PERMIT IMMEDIATE REPLACEMENT OF A DAMAGED OR WORN OUT CATALYTIC ELEMENT. 